Various synthetic polymers, including, but not limited to, polyethylene, PET, polypropylene, polyamides, polyglactin (VICRYL), polyglycolic acid (DEXON), poliglecaprone (MONOCRYL) and poly(L-lactide/glycolide) (PANACRYL), are used to make surgical sutures, including absorbable sutures. Sutures may be smooth, single-strand sutures, or “monofilaments”, or they may be multiple strands woven together, i.e., “braided” sutures. In addition, the desired characteristics of the final suture products, including, but not limited to, tensile strength, absorption rate, elasticity, flexibility and surface morphology, determines, among other things, the type of material that is used to make them, as well as whether they are formed as monofilaments or braided fibers.
During the suture manufacturing process, the suture fibers are produced using one or more formation processes such as extrusion, polymerization, braiding, scouring and coating. As they emerge from the aforesaid formation processes, the suture fibers are often coated with a spin finish, such as a solution of glycerol monostearate and mineral oil (GMS/MO), for the purpose of facilitating further handling and processing of the fibers. The manufacturing process results in the formation of very long fibers coated with a spin finish which are wrapped and/or folded into skeins of more manageable size and shape.
Final coatings, such as caprolactone, polybutilate, polyglycolide, wax and other substances are sometimes applied to suture products for purposes such as providing an outer surface on braided fibers thereby minimizing tissue trauma, increasing the knot tensile strength of the suture, or altering the absorption rate of the suture. Before such final coatings can be applied, however, the spin finish must be removed from the outer surface of the suture fibers.
Efficient removal of the spin finish from suture fibers, especially braided suture fibers, is important because, the spin finish can significantly interfere with the distribution of the final coating throughout the braided fibers if a significant amount of spin finish remains on the braided fibers when the final coating is applied. If the final coating is not able to penetrate the braid and become fully distributed throughout the braided fibers, the resulting braided suture may not meet the required specifications, including, but not limited to, the smoothness of the outer surface, the knot tensile strength or the absorption rate. The efficient removal of the spin finish is the focus of the present invention.
Typically, the spin coating is removed from braided suture fibers by immersing one or more skeins of the suture fibers in an appropriate solvent which is pumped through scouring equipment, such as a conventional scouring bath tank. This method removes the spin coating efficiently from the suture fibers as long as the spin coating is highly soluble in the particular solvent that is used. For example, ethyl acetate is used as the solvent where the suture fibers are made of polyglactin (VICRYL) and the spin finish is made of GMS/MO because GMS/MO is highly soluble in ethyl acetate and, therefore, it will remove a satisfactory amount of the GMS/MO spin finish. If, however, the suture fibers are made of poly(L-lactide/glycolide (PANACRYL) with a spin finish made of GMS/MO, ethyl acetate cannot be used as the solvent because it will attack and destroy the poly(L-lactide/glycolide (PANACRYL) suture fibers. Thus, where the suture fibers are made of poly(L-lactide/glycolide (PANACRYL) having a spin finish made of GMS/MO, isopropyl alcohol is used as the solvent. Unfortunately, GMS/MO is not totally soluble in isopropyl alcohol. Thus, a double scouring process is currently used to remove the GMS/MO from poly(L-lactide/glycolide (PANACRYL) suture fibers, which requires double the time and double the amount of isopropyl alcohol to produce a given amount of suture product than is required for a single scouring process.
With the foregoing in mind, the present invention was developed to increase the scouring efficiency of isopropyl alcohol when used to remove GMS/MO spin finish from braided suture fibers made of poly(L-lactide/glycolide (PANACRYL). It is noted that attempts to increase the scouring efficiency by more conventional methods, including, but not limited to, increasing the fluid flow (i.e., fluid agitation) throughout the tank with a stirring bar and different pumping rates, proved to be unsatisfactory. More particularly, the aforesaid attempts resulted in non-uniform fluid flow within the tank, including the creation of several dead zones, or inactive areas, in which little or no fluid flow occurred.
There have been some notable developments in the wastewater treatment field relating to scouring or cleansing fibrous or filamentary matter with a combined flow of liquid and gas, especially for the prevention of fouling of the filtering membranes of the wastewater treatment devices. For example, WO 98/28066 and WO 00/18498 disclose an apparatus and method for cleaning membrane filtration modules, including membranes made of fibers, as an alternative to conventional backwashing. This disclosure discusses injecting and entraining air bubbles in a liquid stream using a venturi arrangement positioned underneath vertically oriented membranes, such that the air bubbles flow upward along a path parallel to the membranes surfaces requiring cleaning. The membranes discussed in these documents are porous membranes used to filter wastewater and they are arranged such that the surfaces requiring cleaning are oriented vertically. The air bubbles are introduced into an upwardly flowing liquid stream, whereby the air bubbles flow along a path parallel to the membrane surfaces to be cleaned. Thus, by physical scrubbing, the air bubbles remove and prevent fouling of the membranes, i.e., accumulated substances, including solids, particulates, organic matter and biological growth, are removed from the surfaces of such membranes. More particularly, the gas bubbles bump and impact the fibers, thereby loosening and shaking the accumulated solids loose therefrom. It is noted that these references suggest the use of oxygen, air, gaseous chlorine or ozone for the gas.
U.S. Pat. Nos. 5,910,250 and 6,042,677 disclose a baffle used to convert fine aerating gas bubbles in a liquid flow to coarse gas bubbles which then travel upwardly and parallel to the surfaces of vertically oriented fibers to scrub the fibers and remove fouling therefrom. The fibers are hollow fiber membranes, or capillary tubes, and are arranged in a skein and their purpose is to separate a desired permeate from a large body of multicomponent substrate, such as fruit juices to be clarified or wastewater containing particulate matter, especially organic matter. Thus, the air bubbles remove solids and particulates from the fibers by physical scrubbing in which the gas bubbles bump and impact the fibers, thereby loosening and shaking the accumulated solids loose therefrom. In addition, these references specify that the fibers are long enough to sway within a bubble zone, which contributes to the scrubbing action of the coarse bubbles.
U.S. Pat. Nos. 5,192,456, 5,639,373 and 5,783,083 also disclose devices having vertically oriented fibrous membranes for filtration of wastewater and the use of gas bubbles in an upward liquid flow, along the surfaces of the fibers, to prevent and scrub fouling from the fiber surfaces. U.S. Pat. No. 5,192,456 discloses that the gas is introduced into the liquid by an air-blowing pipe and the bubbles are created by a mechanical agitator which stirs the liquid-air mixture. In U.S. Pat. Nos. 5,639,373 and 5,783,083 the gas bubbles are introduced into the liquid flow by air tubes or manifolds with holes, which release the gas as bubbles into the liquid. In these devices, the gas bubbles function to physically scrub solids and particulates accumulated on the fiber surfaces by bumping and impacting the fibers to shake the accumulated solids loose therefrom.
U.S. Pat. No. 5,248,424 discloses a device for withdrawing permeate from a liquid substrate that includes fibers deployed as a substantially horizontally oriented skein. The device also includes a gas distributing pipe having holes that is positioned underneath the fiber skein and the gas bubbles released thereby into the liquid substrate cause the fiber skein to assume an arc shape. Due to the arrangement of the fiber skein and the gas distributing pipe, the gas bubbles travel with the substrate in a direction that is substantially perpendicular to the lengths of the fibers, as opposed to along their lengths as disclosed in the above-discussed prior art references. However, like the above-discussed prior art, the substances to be cleaned from the surfaces of the fibers in U.S. Pat. No. 5,248,424 are solids, including organic molecules and colloidal or suspended solids. In addition, the solids are removed from the fibers by the bumping and impacting action of the gas bubbles on the fibers, thereby shaking the accumulated solids loose therefrom.
The device of the present invention addresses the shortcomings of the existing apparatus and process for scouring coatings off of fibrous materials by improving the agitation of the solvent in a single batch process whereby the solvent is evenly distributed through the fibrous material, thereby minimizing dead zones, maximizing contact of the solvent with the coating on the surfaces of the fibrous material and eliminating the need to perform a double batch process.